Can I enable the use of my laptop's trackball in addition to a USB mouse, and use them at the same time, rather than just the USB or just the trackball?

shouldn't be a problem. assuming you mean in X. i don't know if you'll be able to configure it automatically, but by hand should be pretty straight forward. open up the /etc/X11/XF86Config file and find the existing mouse entry and copy it and rewrite it to reflect the secondary pointer device. then in the serverlayout section add another pointer line for the other device. if you don't know what information to use, back up the existing config file and reconfigure it grpahically wuth Xconfigurator or whatever redhat prefers these days and then see what it's done for you.

Here is the pointer section of my XF86config file... I have a few questions about it. First, what should the new pointer be? /dev/mouse1? How do I create that device? Since I had to custom compile a kernel to work properly with my thinkpad, I have support for both a PS/2 and USB mouse built in. Thank you in advance!

# Pointer section
# **********************************************************************

Section "Pointer"
Protocol "IMPS/2"
Device "/dev/mouse"

# For wheel support - can not be used with Emulate3Buttons
#
# ZAxisMapping 4 5

# When using XQUEUE, comment out the above two lines, and uncomment
# the following line.
# Protocol "Xqueue"

# Baudrate and SampleRate are only for some Logitech mice
# BaudRate 9600
# SampleRate 150

# Emulate3Buttons is an option for 2-button Microsoft mice
# Emulate3Timeout is the timeout in milliseconds (default is 50ms)
# Emulate3Buttons
# Emulate3Timeout 50

# ChordMiddle is an option for some 3-button Logitech mice
# ChordMiddle

EndSection

Also, I thought this was interesting, but might not be important... Anyway, when I unplug the usb mouse and boot the system, I am prompted about a hardware change, and then it allows me to set up the laptop's mouse... But when I log in, then startx, I can't just plug in the USB mouse and go, it never picks it up.... I have USB HID support in the kernel...I'm not quite sure what is up with that...

i couldn't tell you what the usb device would actually be. the /dev/mouse entry will normally be a symlink to /dev/psaux for a ps/2 mouse, and presumably to somewhere else for a usb one but i have so little experience with USB devices....

as X is effectivaly an operating system within itslef as far as device drivers for cards, pointers etc go the mouse configuration used with gpm (when you boot and the change is detected) is completely seperate. The way i'd try to find out what the usb device is going to be is let kudzu or whatever recognise the usb mouse and see what /dev/mouse points to then .. IF it's changed it... check /etc/sysconfig/mouse (i think.. don't quote me) to see what the device is listed there. with both mice connected X should then be able to sue them both.

i have a touch screen monitor and had those two pointers working easily,.

The /etc/sysconfig/mouse shows this:

MOUSETYPE="ps/2"
XMOUSETYPE="IMPS/2"
FULLNAME="Generic 3 Button Mouse (USB)"
XEMU3=no
DEVICE=/dev/mouse

This is with the USB plugged in...